The present invention relates generally to a method for writing servo sector patterns on a data disk storage device, and more particularly, to self-servo writing of servo sector servo patterns on a data disk storage device using a reference pattern on a surface of a data disk.
In many processing and computing systems, magnetic data storage devices, such as disk drives are utilized for storing data. A typical disk drive includes a spindle motor having a rotor for rotating one or more data disks having data storage surfaces, and an actuator for moving a head carrier arm that supports transducer (read/write) heads, radially across the data disks to write data to or read data from concentric data tracks on the data disks.
In general, a magnetic transducer head is positioned very close to each data storage surface by a slider suspended upon an air bearing. Typical clearance between a smooth disk surface and the slider is about one microinch, or less. The close proximity of the head to the disk surface allows recording of very high resolution data and servo patterns on the disk surface. Servo patterns are typically written with uniform angular spacing of servo sectors and interleaved data sectors or blocks. An example servo pattern includes circumferentially sequential, radially staggered single frequency bursts. Servo patterns provide the disk drive with head position information to enable the actuator, such as a rotary voice coil positioner, to move the head from starting tracks to destination tracks during random access track seeking operations. Further, the servo patterns provide the disk drive with head position information to enable the actuator to position and maintain the head in proper alignment with a track centerline during track following operations when user data is written to or read from the available data block storage areas in concentric data tracks on the disk surface.
Data transducer heads currently in use employ dual elements. An inductive write element having a relatively wide recording gap is used to write information into the data tracks, and a read element such as a xe2x80x9cgiant-magneto-resistive sensorxe2x80x9d having a relatively narrow playback gap is used to read information from the data tracks. With this arrangement, data track densities equaling and exceeding e.g. 30,000 tracks per inch are possible.
Conventionally, servo patterns are written into the servo sectors of each disk using a servo writer at a point in the drive assembly process before the hard disk unit is sealed against particulate contamination from the ambient. A servo writer is a complex and expensive manufacturing unit, typically stabilized on a large granite base to minimize unwanted vibration and employing e.g. laser interferometry for precise position measurements. The servo writer typically requires direct mechanical access to the head arm, and includes a fixed head for writing a clock track onto a disk surface.
Because of the need for direct access to the interior of the hard disk assembly of each disk drive unit, the servo writer is typically located within a xe2x80x9cclean roomxe2x80x9d where air is purged of impurities that might otherwise interfere with operation including the servo writing process or in normal usage after manufacturing. Further, such conventional servo-writing methods are very time consuming. In one example, a disk drive having two disks with four data storage surfaces can require three servo-writer-controlled passes of the transducer head over a single track during servo writing, consuming a total servo writing time as long as 13.2 minutes. Thus, servo writing using servo writers in clean rooms requires both considerable capital investment in the manufacturing process and severe time penalties in the manufacturing process attributable to servo writer bottlenecks. Further, as track densities increase with evolving hard disk designs, servo writers become obsolete, and have to be replaced, or upgraded, at considerable capital expense.
An attempt to alleviate the above shortcomings is directed to servo writing a master pattern at full resolution on one surface of a master disk during a pre-assembly operation. Then, a master disk with the master pattern is assembled with other blank disks into a disk drive unit. After the disk drive unit is sealed against the ambient, the master servo pattern of the master disk is used as a reference by the disk unit in self-writing embedded sector servo patterns on each data surface within the enclosed unit. Finally, the master pattern is erased, leaving the disk drive unit with properly located embedded servo sector patterns on every surface, including the surface which originally included the master pattern. An example of this servo writing method is described in U.S. Pat. No. 5,012,363 to Mine et al, entitled: xe2x80x9cServo Pattern Writing Method for a Disk Storage Devicexe2x80x9d. However, a disadvantage of such a method is that certain repeatable run out information must be removed during the self-servo write operation. Another disadvantage of such a method is that a number of expensive servo writers are still required to write the master patterns on the master disks.
A self-servo writing method which eliminates the need for such servo-writers is described in commonly assigned U.S. Pat. No. 5,668,679 to Swearingen et al., entitled: xe2x80x9cSystem for Self-Servo writing a Disk Drivexe2x80x9d, the disclosure thereof being incorporated herein by reference. That method essentially comprises the steps of writing a clock track at an outside diameter (OD) recording region of a first disk surface of a disk drive having multiple storage surfaces, tuning an open-loop seek from the OD to an inside diameter (ID) recording region to develop a repeatable seek profile, and recording a plurality of high frequency spiral tracks from the OD to the ID, each spiral track including embedded (e.g. missing bit) timing information. Then, spiral track provided peak data, and missing bit data, are read back. A voltage controlled oscillator is locked to the timing information to track disk angular position. As the head is then moved radially from OD to ID the detected spiral peaks shift in time relative to a starting (index) mark, although the timing information does not shift. Embedded servo sectors can then be precisely written across the data storage surface by multiplexing between reading spirals and writing servo sectors (wedges). After the integrity of the wedges has been verified, the spirals are erased (overwritten with user data). While this method is satisfactory, challenges remain in generating and recording an accurate clock pattern on the first disk surface. Further, the time period required to produce the master position pattern on the first disk surface can be lengthy.
There is, therefore, a need for an improved self-servo writing method in disk drives which reduces self-servo writing times, is simpler to implement and does not require servo-writers.
The present invention satisfies these needs. In one aspect, the present invention provides a method for self-servo writing a disk drive by transferring a servo reference pattern onto at least one storage surface of a disk. The servo reference pattern is transferred onto the storage surface by magnetic printing, wherein a resulting printed reference pattern comprises servo clock information providing transducer head circumferential relative position information, and servo position information. The servo position information includes coarse position information for providing transducer head coarse radial relative position information, and fine position information for providing transducer head fine radial relative position information. The printed reference pattern has a resolution lower than that of a disk drive servo pattern features proportional to head gap widths of data transducer heads included in the disk drive. The disk drive is assembled, including installing the disk into the disk drive and enclosing the disk and the data transducers within a housing.
Thereafter, in a self servo writing process, the printed reference pattern is read from the disk via transducer heads, and the read servo clock and the servo position information are used to precisely position and maintain the data transducers at concentric track locations of disk storage surfaces of one or more disks. Servo patterns are self-written onto the storage surfaces at the concentric track locations with the data transducers in accordance to said disk drive final servo pattern features.
In one example, the clock information comprises a pattern of one or more substantially radial timing segments, and the servo position information comprises slanted segments, such that sets of one or more timing segments are separated by the slanted segments. In one case, the slanted segments between the timing segments include periodically suppressed slanted segments, wherein the coarse position information comprises the periodically suppressed slanted segments, and the fine position information comprises the unsuppressed slanted segments. As such, the fine position information comprises a fine pattern of slanted segments, the coarse position information comprises a coarse pattern of slanted segments, the coarse pattern of slanted segments being interspersed with the fine pattern of slanted segment, and sets of one or more timing segments are separated by said interspersed coarse and fine patterns of slanted segments.
In another case, the servo position information comprises slanted segments, such that sets of one or more timing segments are separated by the slanted segments, wherein the slanted segments between the timing segments are organized into at least two circumferentially adjacent sets of transverse slanted segments. The slanted segments between timing segments include periodically suppressed slanted segments and wherein the coarse position information comprises the periodically suppressed slanted segments, and the fine position information comprises the unsuppressed slanted segments.
In self servo-writing the disk drive, the coarse position information can be used to measure a dominant component of eccentricity of the printed reference pattern. Further, the fine position information in conjunction with the clock information and the coarse position information of the printed reference pattern can be used to precisely position and maintain the data transducers at concentric data tracks.